The Jet Propulsion Laboratory in Pasadena, California, has selected Martin Marietta Aerospace, Denver Division in Colorado and the Space and Communications Group, Hughes Aircraft Co., El Segundo, California to conduct studies which could lead to development of an unmanned NASA spacecraft to make topographical radar maps of Venus in the mid-1980s.

When the $500,000 study contracts are completed next summer, one of the two companies may be chosen to develop the Venus Orbiting Imaging Radar spacecraft if the mission is approved by Congress.

Planned for Space Shuttle Launching and five month trip to Venus, the spacecraft would first be placed in 300 by 19,000 kilometer (185 by 11,000 mile) Venutian orbit for two-month gravity study of the planet.

The craft's orbit would then be circularized at 300 kilometers (185 miles) for 120-day radar mapping sequence, which would cover nearly all the surface of Venus at low resolution, 1.0 kilometer (0.6 mile), and about 2.5 percent at high resolution, 100 meters (328 feet).

The primary mapping instrument aboard the spacecraft will be side-looking synthetic aperture radar similar to one flown in 1978 aboard NASA's experimental oceanographic satellite, Seasat.